Thallium and FDG PET Provide Incremental Viability Information to Transesophageal Dobutamine Echocardiography for Identifying Hibernating Myocardium In asynergic myocardial regions with preseved myocardial blood flow (MBF) at rest, contractile reserve may be unmasked by low-dose dobutamine. However, in regions rendered dysfunctional by chronic hypoperfusion, we hypothesized that the administration of a positive inotropic agent (even at low doses) may produce myocardial ischemia and persistent regional dysfunction. To determine whether thallium (Tl) scintigraphy and positron emission tomography (PET) provide additional viability information beyond that of dobutamine (D) transesophageal echocardiography (TEE), we studied 10 patients with chronic CAD and impaired LV function at rest (LVEF ranged from 11 to 44%, mean = 30%). All pts underwent baseline and D-TEE, stress-redistribution-reinjection Tl imaging and PET at rest using N-13 ammonia and F-18 deoxyglucose (FDG). For each patient, the LV was divided into 12 regions and D-TEE, Tl and PET data were compared. Absolute MBF (ml/g/min) was computed for a single large region in which ammonia uptake was uniform and all other regions were then scaled by this MBF value. Among 78 regions with reduced MBF (<0.7 ml/g/min) and asynergy at rest, 41 (53%) improved during D-TEE. Thirty-nine of the 41 (95%) were confirmed as viable both by Tl and PET. However, among the 37 regions that did not improve during D-TEE, 16 (43%) had normal or reversible Tl defects and 21 had irreversible Tl defects (7 mild-moderate and 14 severe). PET confirmed viability in 15 of the 16 Tl viable regions. In addition, PET identified viable myocardium (FDG:MBF mismatch) in 5 of 14 (36%) severe irreversible Tl defects. These data suggest that in asynergic regions with abnormal blood flow at rest (hibernating myocardium), when contractile reserve with D-TEE is present, myocardial viability is established and additional testing with Tl and/or PET is not required. However, in the absence of contractile reserve with D-TEE, Tl and FDG PET provide significant additional information regarding myocardial viability.